/**
 * Simple downsample shader. Takes the average of the 4 texels of lower mip.
 **/

uniform samplerCube source;
uniform float texelSize;

flat in int fFace;

out vec4 FragColor;

const vec3 maj_axes[6] = vec3[6](vec3(1.0,  0.0,  0.0), vec3(-1.0,  0.0, 0.0), vec3(0.0, 1.0, 0.0), vec3(0.0, -1.0,  0.0), vec3( 0.0,  0.0, 1.0), vec3( 0.0,  0.0, -1.0));
const vec3 x_axis[6]   = vec3[6](vec3(0.0,  0.0, -1.0), vec3( 0.0,  0.0, 1.0), vec3(1.0, 0.0, 0.0), vec3(1.0,  0.0,  0.0), vec3( 1.0,  0.0, 0.0), vec3(-1.0,  0.0,  0.0));
const vec3 y_axis[6]   = vec3[6](vec3(0.0, -1.0,  0.0), vec3( 0.0, -1.0, 0.0), vec3(0.0, 0.0, 1.0), vec3(0.0,  0.0, -1.0), vec3( 0.0, -1.0, 0.0), vec3( 0.0, -1.0,  0.0));

float brightness(vec3 c)
{
	return max(max(c.r, c.g), c.b);
}

void main()
{
	vec2 uvs = gl_FragCoord.xy * texelSize;

	uvs = 2.0 * uvs - 1.0;

	vec3 cubevec = x_axis[fFace] * uvs.x + y_axis[fFace] * uvs.y + maj_axes[fFace];

	FragColor = textureLod(source, cubevec, 0.0);
}
